1. Field of the Invention
The present invention relates to new polyurethanes which contain acryloyl groups and can be converted into crosslinked products by radiation curing and to a process for their preparation.
2. Description of the Prior Art
Polyurethanes which contain acryloyl groups and are known and may be obtained, as described, for example, in DE-OS (German Published Specification) 1,644,798, DE-OS 2,115,373 or DE-OS 2,737,406, as the reaction product of, inter alia, polyisocyanates and hydroxyalkyl acrylates. They are cured with the aid of high-energy rays, such as UV rays or electron beams, and are used for coating, for example, wood or for the production of coatings for graphical purposes.
These so-called urethane acrylates have a high viscosity. To reduce their viscosity, polyether alcohols are often used for their preparation, in addition to hydroxyalkyl acrylates. However, even if only (cyclo)aliphatic polyisocyanates are employed, the resulting products are not stable to weathering.
An object of the present invention is to provide aliphatic polyurethanes containing acryloyl groups which have viscosities suitable for processing as surface coating binders without the necessity of incorporating ether groups into. It is an additional object of the present invention to provide aliphatic polyurethanes which are distinguished by a high reactivity under UV irradiation.
These objects may be achieved by providing the aliphatic polyurethanes containing acryloyl groups according to the invention which are described in more detail below.